The present invention relates to safety latches for locking a data transducer assembly against inadvertent movement across a data storage surface within a rigid disk data storage device. More particularly, the present invention relates to a safety latch which locks the data transducers at their landing zones on the disk surfaces except when a sufficient airflow is generated by disk rotation as to release the latch and thereby enable the transducers to leave the landing zone region.
Rotating rigid disk magnetic storage devices (sometimes referred to as "drives") typically utilize data transducers which fly upon an air cushion immediately adjacent to the storage surface. The transducer is held just above the surface by an air bearing effect. This technique, widely used in presently known disk drives, is sometimes referred to as "Winchester technology".
In disk drives employing Winchester technology the data transducers are supported by a carriage assembly which is normally biased to position the transducers at a predetermined landing zone on the disk storage surface. In some cases the landing zone is located inside the innermost annular data storage track of the storage surface. This bias is normally always present, and it is typically provided by a tension spring. In use of the drive, the bias is overcome by the forces applied by the carriage driving mechanism. In some cases, the driving mechanism may be a linear translator such as a linear voice coil solenoid. In other cases the driver may be a stepper motor or a rotary actuator. In any event, when power is removed, or when the storage disks are not rotating at their normal operating speed, the driver becomes disenabled, and the bias spring automatically returns the transducers to the landing zone region of the disk storage surfaces.
The disk storage surface is typically coated with a very thin magnetic material which stores the recorded data for later retrieval and/or replacement. The storage surface is packed with very high data densities, on the order of 10,000 bits or more per inch. The storage surface is particularly sensitive to being damaged. Any minute scratch or indentation may deform the storage surface, with resultant loss of data and data storage capability at the damage site.
The movement of a data transducer across the recording surface in the absense of the air bearing or cushion may result in damage to the storage surface from minute scratches or dents. The damage or deformity is caused because of a loading force provided to the transducer to urge it against the disk surface. The loading force is opposed to the force generated by the air bearing effect. The loading force is provided with a value which causes the transducer to come within 12 to 20 microinches of the storage surface during operation.
When the drive is not in operation, the loading force applied to the transducer may be sufficient to dent or gouge the storage surface in the absense of the protective air cushion. Also, the storage surfaces may be dented if the transducers are susceptible to severe, complex rotational and/or translational forces sometimes encountered during unusually rough shipping and handling. As disk drives become smaller, and as they move through commerce by common carriers unaccustomed to handling delicate instruments, such drives have become susceptible to storage surface damage arising from severe handling.
The most common damage sustained by severe handling has been denting of the storage surface. Such dents are caused by severe shock forces having substantial components normal to the parallel planes of the disk surfaces. As already mentioned, such dents are known to prevent the drive from storing data at the locations thereof. If such dents occur during shipment and/or handling between the factory and the user, their presence will go undetected until data storage errors are encountered by the user.
The requirement to lock the data transducer assembly of a rotating rigid disk data storage device during shipment and handling is recognized in the prior art. There are three general approaches: manual mechanical locking devices; solenoid safety latches which are disengaged only when the drive is in operation; and, permanent magnet latches which lock the assembly against movement in response to shocks below a threshold force level.
Manual locks are unsatisfactory because they require the intervention of an informed user. If the user is unaware of the manual lock, an attempt to use the drive may result in overload and damage to the transducer actuator. Conversely, the user must remember to engage the manual latch to prevent damage during shipments subsequent to original delivery. Solenoids are usually effective, but they add additional cost and power consumption overhead. Permanent magnets are only partially effective. They have the drawback that very severe shocks to the drive will overcome the locking force, leading directly to the infliction of the damage sought to be avoided.
One drawback of Winchester disk drives is that the unit must be assembled and operated in a very clean, dust free environment. Once assembled, the drive is enclosed within a hermetically sealed housing to protect against intrusion of unfiltered ambient air. This ultra-clean environment renders impractical the use of temporary, removeable locking members or devices to lock the actuator assembly within the disk drive enclosure.
One prior art approach is set forth in U.S. Pat. No. 3,503,056 which describes an aerodynamically operated microswitch for controlling a motor for lowering data transducers into operational position only after sufficient air velocity has been generated to deflect a vane which actuates the switch. This approach requires not only the air vane, but also complex electrical machinery which must be precisely aligned and operated.
Another prior art approach is followed in U.S. Pat. Nos. 3,172,962 and 3,180,943 wherein aerodynamic flow from rotation of a data storage drum operates a lever which lowers the data transducer into operating proximity relative to the data storage surface. That approach is not feasible in disk drives characterized by fixed transducer support arms which include bias springs applying a predetermined loading force to the data transducer, and wherein the data transducer is adapted to contact the storage surface at the landing zone (and anywhere else on the disk surface, absent the air bearing cushion).
A need has therefore arisen to provide a more satisfactory locking mechanism which will lock the data transducer assembly at a safe position whenever severe mechanical forces or shocks might be encountered, and which will release to enable normal operation of the drive when the storage disks are rotating.